In a conventional type of radio receiver, it is not easy to make a determination as to whether a received signal is an analog modulation signal or a digital modulation signal. An analog/digital receiver which can automatically discriminate between analog modulation and analog modulation and output a demodulation signal corresponding to an incoming signal is disclosed, for instance, in Japanese Patent Laid Open Publication No. 154534/1990.
The analog/digital receiver disclosed in Japanese Patent Laid Open Publication No. 154534/1990 comprises a radio receiving section which converts a received signal first to a signal having an intermediate frequency and then amplifies the signal, or directly amplifies the received signal, an analog demodulating section as well as a digital demodulating section each connected in parallel to an output terminal of the radio receiver, and a switch which switches output from the analog demodulating section as well as from the digital demodulating section, converts the electric signal output from the switch to sound at a sound convert section and outputs the sound.
Also provided in the digital demodulating section is a detecting section for detecting the presence of a synchronizing signal, switching the switch to the output of the digital demodulating section when a synchronizing signal is detected in the detecting section, and disconnecting the output from the analog demodulating section.
With the configuration as described above, even if an analog modulation signal or a digital modulation signal is received at random, which type signal is received, an analog modulation signal or a digital modulation signal, is automatically discriminated, and the output from a demodulator correctly corresponding to the input signal is outputted.
As described above, in the conventional type of analog/digital receiver, the presence of a synchronizing signal is detected by a detecting section provided in a digital demodulating section to determinate as to whether a receiving input is an analog modulation signal or a digital modulation signal, and generally when demodulating a digital modulated signal, a long time is required for detection because determination is difficult unless the received data is demodulated by regenerating the clock. As a result, a disadvantageously long time is required until, e.g., an aural signal is output.
Also when receiving signals for many channels within a short period of time in a scanner receiver, the conventional technology as described above is not suited to, and is not practically available for, receiving and detecting a digital demodulated signal.